This invention relates to a magnetic bearing used, for example, in a magnetically levitating apparatus and, in particular, a non-linear control type magnetic bearing.
A variety of magnetic bearings utilizing the attractive force of electromagnets have recently been developed, but this type of magnetic bearing is, in general, very expensive, since a position displacement sensor and power amplifier necessary for magnetic bearings are much higher in cost and greater in dissipation power. If these drawbacks are overcome, then it may be considered that such magnetic bearings having a contactless, non-friction and oilless feature will find a wider range of practical application.
In the field of a linear control method, a magnetic bearing has already been implemented and commercialized which utilizes a velocity sensor using an inexpensive, easy-to-manufacture search coil in place of the expensive position displacement sensor. It is disclosed in, for example, "Magnetic Suspension with Passive Radial Centering for Satellite Flywheel and Kinetic Energy Storage Systems", the Third International Workshop on Rare Earth-Cobalt Permanent Magnets and Their Applications, June 27 to 30, 1978 by P. C. Poubeau. This system also has advantages as a "zero-power" system and has already been established as such. However, this system has a drawback that it cannot start to levitate an object from an at-rest position. For this reason, an extra lift-off circuit is provided so as to levitate the object. It is therefore necessary to provide another sensor corresponding to the position displacement sensor. This is a substantial bar to a wide acceptance of this system.
A general non-linear type control theory is disclosed in "Theoretical Basis of Technical Cybernetics" and "Optimal Quick-Action Line System", 1966. However, this theory has not been applied to magnetic bearings so far.